Engine operating parameters such as air-fuel ratio, spark timing, and exhaust gas recirculation (EGR) may be adjusted to increase engine efficiency and fuel economy and decrease emissions including nitrogen oxides (NOx). One factor which may affect the adjustment of such operating parameters is intake air humidity. A high concentration of water in the intake air may affect combustion temperatures, dilution, etc. Therefore, control of operating parameters including air-fuel ratio, spark timing, EGR, and the like based on humidity can be used to improve engine performance.
U.S. Pat. No. 6,725,848 describes a method for determining intake air humidity using a humidity sensor located in the intake manifold or charge air cooler. However, humidity sensors may be inaccurate under certain conditions and/or prone to degradation when exposed to high engine operating temperatures.
The inventors have recognized the issues with the above approach and provide a method to at least partly address them. In one embodiment, an engine method comprises adjusting an engine parameter in response to intake air humidity estimated based on a concentration of one or more engine-out emissions.
For example, exhaust NOx and/or particulate measurements may be compared with expected NOx and/or particulate levels, respectively, for a given humidity level in order to determine current humidity conditions. In this manner, the effect of intake air humidity on various operating parameters may be reduced.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.